Regulation of na channels in the rat cortical collecting tubule:
effects of camp and methyl donors.
Frindt, Gustavo, and Lawrence G. Palmer.
Dept. of Physiology and Biophysics, Cornell University Medical
College, 1300 York Ave., New York, NY 10021
APStracts 3:0145F, 1996.
The whole-cell patch-clamp technique was used to investigate the
interactions of the amiloride-sensitive Na channel of the rat
cortical collecting tubule with cAMP and with methyl donors. The
amiloride-sensitive whole-cell current (INa) was measured in
principal cells of dissected, split-open tubules from rats maintained
either on a control diet or on a low-Na diet to increase endogenous
aldosterone secretion. With Na-depleted animals, INa was highest
immediately after rupture of the membrane patch, and averaged 325 pA
at a membrane potential of -60 mV. INa declined over 15 minutes to
35% of the initial value. With 8-cpt-cAMP in the pipette, INa
increased within 5 minutes of membrane rupture and was maintained for
15 min at levels 3-4 fold higher than the corresponding control
values. With Na-replete animals, INa was undetectable (< 10 pA)
without cAMP. With cAMP in the pipette INa averaged 40 pA. In cell
-attached patches on tubules from Na-replete rats exposed to cAMP,
single Na channels were observed with conductive and kinetic
properties similar to those from Na-depleted rats but at lower
density. Inclusion of the methyl donor s-adenosyl methionine to the
pipette solution did not increase INa in CCT's from Na-replete rats,
either in the presence or absence of cAMP. The methylation inhibitor
S-adenosyl homocysteine did not affect INa in CCT's from Na-depleted
animals.
Received 20 March 1996; accepted in final form 19 August 1996.
APS Manuscript Number F93-6.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 29 August 1996